1. Learning Aid: Technical Terms for Describing Drawings
(How to say what you see)
Skills Exploration : Electronics and Robotics

2. Why Words?
Tradespeople, Technicians and Engineers use drawings every day
Drawings are the “language of technology”
A good technical drawing can be understood anywhere around the world!
Knowing the language helps you communicate clearly
Using the correct words makes you sound skilled
Describing a drawing helps you think about how to create a drawing
Complex drawings have to be broken down into simple steps
The shapes we will describe and draw today are simple
But the thought process is not
It requires care and attention to detail… important skills in the work world!

3. You already know many of the words…
Square
Rectangle
Triangle
Circle
Line
Point
Vertical
Horizontal

4. You probably know these ones, too…
Perpendicular
Two lines “at right angles”
Also known as 90 degrees
Parallel
Two lines that run in the same direction
But don’t overlap
Concentric
Sharing the same centre point
Collinear
Line segments that are “on the same line”

5. Ellipse A distorted circle It has a “Major Axis” (the long side)
Minor Axis
Major Axis
A distorted circle
It has a “Major Axis” (the long side)
And a “Minor Axis” (the short side)
Minor Axis
Major Axis

6. Arc A section of a circle or ellipse Can also be called a curve
But curves can be more complex, and made of many arcs.

7. û ü Tangent Where a line touches a curve at only one point
It may not cross the line… only touch it! û ü

8. Fillet Rounding the corner where two lines meet
Uses a circular arc tangent to the two lines

9. Chamfer Cutting the corner where two lines meet
Like a fillet, but with a straight line rather than a circular arc
Chamfers and fillets are often used to remove sharp edges from objects

10. Offset Drawing a similar shape, but off to one side of the original
Can be applied to lines, curves, circles, squares, ellipses or even PacMan
Offset
PacMan
Original
PacMan
Offset
Arc
Original
Arc
Offset
Arc
Original
Line
Offset
Line

11. Angles and Rotation
90°
60°
45°
Sometimes a shape is rotated or a line is at an angle
We use the same “degrees” of rotation that you use in math class
There are 360° in a circle
90°, 45° and 30° are all common angles
This compass is marked in 5° increments
30°
180° 0°
270°

12. How would you describe this shape?
There is a square
It is not rotated
There is a circle
Centred on the top left corner of the square
It has a radius about one quarter the length of the side of the square
There is a line
It goes from the top right corner of the square to the bottom left corner of the square

13. Try drawing this shape…
There is a triangle
All the sides are the same length
The bottom of the triangle is horizontal
There is a circle at each corner of the triangle
The radius of the circle is about one third of the side of the triangle
The top circle and left circle are joined with a line
The line is tangent to both circles

14. Try describing this shape…
There is a rectangle
It is about twice as long as it is high
The long edge is rotated about 20° from horizontal
Inside the rectangle is an ellipse
The edges of the ellipse are tangent to the sides of the rectangle
There is a line to the left of the rectangle
It is parallel to the short edge of the rectangle
It is the same length as the short edge of the rectangle
It is offset from the short edge of the rectangle by about one tenth of the length of the long edge of the rectangle

15. Can you draw this shape? There are three concentric circles
If the first circle has a radius of 1 unit
The second circle has a radius of 1.5 units
The third circle has a radius of 2 units
There is another circle
Its centre is about 4 units to the left
And 3 units above the centre of the first circles
It has a radius of 2 units
The 2-unit circles are joined by two lines
One line is tangent to the tops of the big circles
The other line is tangent to the bottoms of the big circles
The two tangent lines are connected by a line
It is perpendicular to the tangent lines
It is located at the midpoint of the tangent lines (halfway)

16. Now find a partner….
Arrange the desks/chairs so that one partner has their back to the screen
The partner with their back to the screen should be able to draw
The other partner can see the screen
But not what their partner is drawing.
Perhaps arrange the chairs to place the partners back-to-back
The partner who is looking at the screen is going to describe a drawing to their partner, who will attempt to draw it
Ready?

17. Try describing this to your partner…
Start with a square
It is rotated 45°
The top right side of the square forms the base of a triangle
One side of the triangle is a vertical line, extending up from the right hand point of the square.
The other side of the triangle is a horizontal line, extending to the right from the top of the square
The tip of the triangle is filleted, with a radius about 1/3 of the length of the triangle sides
The bottom left side of the square forms the base of another triangle
This triangle points in the opposite direction from the first triangle
This triangle is “pointier” than the first triangle
The angle of each side of the triangle is about 30° from the base of the triangle
The tip of this triangle is chamfered
About 1/5 of the way from the tip of the triangle
Inside this triangle is a circle
It is tangent to the two sides of the triangle
It doesn’t quite touch the chamfer, but it comes close

18. Now the partners swap positions….
Get a fresh sheet of paper for the student doing the drawing.
Ready?

19. Try this one…
There are three circles of equal diameter stacked vertically
The top edge of one circle is tangent to the bottom edge of the next circle
The middle circle has three smaller concentric circles inside it
Their diameters are about 75%, 50% and 25% of the larger circle
The left sides of the three large circles are joined by a line
The line is tangent to each of the circles
It extends from where it touches to top circle to where it touches the bottom circle
There is a line that is perpendicular to this line that passes through the centre of the middle circle
It begins where the vertical line touches the middle circle
It has a length about twice as long as the diameter of the three large circles

20. Okay… just one more
It will be easy if you remember what a “tangent” is
Let the best “drawer” draw, and the best “describer” describe…
Ready?

21. The Last One… There is a square Inside the square is a curve
It is not rotated
The top corners are filleted
The fillet radius is about 1/5 of the length of the side of the square
Inside the square is a curve
It touches the square at:
The bottom left corner
It is tangent to the bottom side of the square
The midpoint of the top side
It is tangent to the top side
The bottom right corner
It is tangent to the bottom side

22. How would you like to describe this drawing?
We’ve been using simple, abstract shapes because real things become complex quickly.
This is actually a design for building a simple electric motor
It gets cut on a CNC machine and the two end pieces are rotated vertically to fit into the rectangular slots.
Bearings and a shaft go into the round holes
Magnets and brushes mount to the elongated slots
You could do it … but it would be a pain!
“A picture is worth a thousand words.”
More importantly, a picture can be understood in any language
Knowing the words to describe drawings can help you discuss drawings
You can suggest changes … or understand suggestions to improve your design
Knowing the process to break a shape into smaller parts can help you create complex drawings
Using detailed, specific terms can help you produce better instructions
Clear, precise communication is an important skill that can be learned!